1. Field of the Invention
The present invention relates to a pattern recognition method.
2. Description of the Prior Art
In recent years, techniques associated with pattern recognition have been remarkably advanced. The pattern recognition techniques are utilized in a variety of fields such as reading of characters or figures, recognition of shapes of articles, dimensional measurement of articles, and the like.
For example, in the field of manufacture of a semiconductor device, a pattern recognition technique is utilized for measuring a line width of a resist film formed on a semiconductor wafer. The line width of the resist film is measured as follows. First, a semiconductor wafer is irradiated with light. Light reflected by the wafer is imaged by a two-dimensional camera or the like, thus obtaining image data associated with the intensity and coordinates of the reflection light. In this case, the sectional shape of resist film 11 is as shown in, e.g., FIG. 1. More specifically, side wall portion 11a of resist film 11 is moderately extended outwardly. Therefore, light interference occurs at the edge portion of resist film 11. A signal based on light causing interference at the edge portion of resist film 11 varies with noise. For this reason, the line width of resist film 11 is calculated with reference to a portion indicating an intermediate light intensity between a light intensity on the resist film 11 portion and a light intensity on a substrate portion immediately below resist film 11.
However, in the field of manufacture of a semiconductor device, the degree of integration has been improved. For example, a wiring pattern constituting an integrated circuit tends to be micropatterned to 1 .mu.m or less. In contrast to this, a conventional pattern recognition method cannot perfectly eliminate an error based on light interference as described above. As a result, in the conventional method, the above-mentioned very small line width cannot be accurately measured.
When the line width of resist film 11 is to be measured, it is important to determine the line width (bottom value) at a bottom portion of resist film 11 contacting the substrate. However, in the conventional method, the line width as the bottom value is calculated based on an average value of light intensities reflected by the inclined side surface of resist film 11. As a result, when the pattern of resist film 11 changes, a difference between the line width value of resist film 11 measured by the conventional method and a line width value based on a true bottom value is increased.
In order to eliminate the above problem, the very small line width of resist film 11 is measured using a scanning electron microscope (SEM). In this case, however, a large-scale SEM is required. In addition, in order to measure a line width, much labor and time are required, and the conventional method is not suitable for mass-production.